1. Field of the Invention
The present invention is directed to an electron generating assembly for an x-ray tube, of the type having a cathode and an electrode system for accelerating the electrons emitted from the cathode.
2. Description of the Prior Art
X-ray tubes are known that have an electron generating assembly with a helical or serpentine cathode as the electron emitter formed by tungsten wire. This tungsten wire must be heated to high temperatures for the emission of electrons, particularly when high electron current densities must be achieved. Tungsten evaporates at these temperatures and becomes brittle, the useful life of the X-ray tube being limited as a result. Moreover, a coating of tungsten is formed on the inside wall of the glass enclosure of the X-ray tube with usage over time, this likewise being undesirable.
For extending the service life of an X-ray tube, German 40 26 298 disclosed an x-ray tube wherein the electron emitter is manufactured of a cathode material having a low electron affinity. As a result, the cathode temperature can be lowered given the same electron emission, and thus the service life can be extended.
German Patent 331 424 discloses a Lilienfeld tube, particularly an X-ray tube, having a drilled electrode, electrons being triggered at the walls of the opening on the basis of a primary event. The primary event is triggered by a primary discharge that occurs between an incandescent lamp and the X-ray cathode. As many electrons as possible are intended to be triggered for each electron absorbed by the cathode on the basis of the fashioning of the opening.
In an article "Optically Switched Pulsed X-ray Generator," Ziegler et al. The Review of Scientific Instruments, Vol.43, No. 1, January 1972, pp. 167 and 168, an x-ray generator is described having an electron generating assembly that a cold cathode formed by a photocathode which emits electrons controlled by a light source, an electron multiplier, and an electrode system for accelerating and focussing the electrons emanating from the photocathode onto an anode.